By design, Bitcoin is scarce - there will only be 20999999.9769 bitcoins ever made.
Contrast that with USD where more and more money is being printed or added to the system via:
quantative easing
increasing federal debt ceiling
So that is one factor.
The other is simple supply and demand - more and more people want to invest in bitcoin for speculative reasons, not as a means to buy goods and services but to heard in hopes that the price is going to continue going up.
That removes even more bitcoins from circulation, driving the price even higher.
To sum up: supply of bitcoin is limited by design, the shortages are made worse by speculators.
It's not too different from speculators driving iPhone or Nintendo prices up on secondary markets.
Same can be said some cars and many luxury good in general - look up veblen goods.

It is one of the basic pillars of bitcoin that the supply is limited, it is unlikely that a fork which minted new coins would be accepted, you can create a fork but that fork is not bitcoin. 1 Bitcoin is divisible by 100,000,000.

I agree. The bitcoin number limit is fundamental. It's what shows up fiat for what that is. It's also what makes it threatened. I believe the growth of altcoins was in part to placate the financial system. Maybe not increase the total number of bitcoin that will ever exist but the creation of altcoins gives the idea that the alternative to fiat is expanding as fiat multiplies.

I don't think that means it isn't scarce: if there was a supply of water (and you could buy it in any amount) and people were buying it up and selling it on a secondary market, it would still cause the price to go up.

That's fine, I'm not talking about the price. I just mean its not really scarce when you can divide it up so much and trade it. The scarcity is fake. It's like saying there is only 10 trillion dollars in a bank so the trillions are scarce if I'm only going to trade 1 trillion at a time.

CME has announced they intend to introduce a Bitcoin Futures product. If this is allowed it will allow institutional investors (think pension funds, hedge funds etc) to legally indirectly invest in bitcoin.

The amount of money in the hands of institutional investors is huge, multi hundred billions. If a minuscule numbers of these investors put a tiny amount of their portfolio in bitcoin, the price will rocket even further.

Because it provides a highly uncorrelated alternative to both (1) precious metals like gold and (2) sound currencies like the US Dollar and the Euro. Bitcoin will coexist with them for as long as the Internet exists and encryption works.

Here's a link to something I wrote in 2011 about Bitcoin's potential for long-term price appreciation -- in it I mention not only Zimbabwe's longtime issues with money, but also those of other countries, including Argentina in the early 2000's, Belarus in the years leading to 2002, Bolivia in the mid-1980’s, Brazil in the early 1990’s, Indonesia in 1997, Mexico in December 1994, Poland circa 1991, Russia in August 1998; South Korea in 1997, Thailand in 1997, and Yugoslavia in the early 1990’s. This is far from a complete list of countries that have had major currency problems. Currency crises are pretty common as you go back in history.

There is yet another Bitcoin fork (seg2wit) coming. If you hold BTC at the time of the fork you might get free money like with the last fork (bitcoin cash). If and when it will fall? Hard to predict, but it sure looks like a Ponzi scheme.

This fork is Segwit2x, and is considered to be an adversarial fork -- some even consider it the first battle in a civil war. The 'dividend' of getting free money does not apply here. In fact, a lot of folks in the Bitcoin community think that the price of BTC is actually signficantly _depressed_ because of this uncertainty. It's almost certainly not contributing to the price rise.

Here you can see how long it takes to double or get 10x bigger. And you see that at times bitcoin did grew faster (the curve was steeper at some moments). You also see that the corrections were bigger... so volatility does seem to decrease (until now).

So it is not new that is grows fast. Why it does grow fast? I prefer to let this question open. There are many different possible answers. Maybe the actual system has no solid fundamentals? (if every runs to the bank, the is not enough there for everybody o_o). Or the younger libertarian generation prefer it to gold? Or it could bank the unbanked of this world (once lightning implementations in bitcoin and other improvements are past alpha/beta stadium)? Or because venezuela might not be the last state with hyperinflation and cryptocurrencies might be the alternative (once scaling through lightning/... is improved)? Or a new way for machines to exchange with each other?

Obviously speculation on some of these (and other) reasons is still dominating... but it may mean that people seem to belive these secenarios might happen

In a way, the same problem exists with Bitcoin where the supply is basically a fixed quantity that expands at less than 1% a year while the number of those wanting to speculate in it, expands like a pyroclastic eruption. This drives the price ever higher, increasing volatility and making it even less likely that anyone would adopt it for normal transaction activity. The participant speculators smack their lips while they drive their protege currency further and further away from it’s intended purpose. The same thing happens in conventional Mining stock promotion, the price of the stock becomes the material and tangible nature of the enterprise while the plans, potential and possibilities of the ore body, the very thing that speculators should be considering, become more and more amorphous and immaterial. In simple terms, the cart is before the horse.

The success of bitcoin (amongst other cryptocurrencies) has led to great investor interest in blockchain techologies. Investments in these technologies are generally made by way of an ICO, usually denominated in bitcoin and/or ether. This increases demand for bitcoin & ether which raises the price and generates even more investor interest in blockchains/cryptocurrencies, leading to further ICO's and so on.

There are of course speculators, and an increase in the number of businesses accepting bitcoin for regular transactions, but I suspect the ICO boom is likely the driver behind the recent spike.

I've said this before, my non-educated analysis of the situation... There is no reason for it not to go up..there is a finite amount and people are buying because its going up. Each time someone buys bitcoin it goes up because typically people are only going to sell above what they paid. It's not a stock, there isn't a huge company behind bitcoin trying to satisfy people. It's a store of value and a way of transferring value. The only reason it would go down is if the network gets hacked or the government makes laws against it or some pure panic situation (which has happened before). Other than that why would something like bitcoin drop? People stop being interested but with the price going up and the news coverage it advertises itself.

It's trust: if people in general stop trusting Bitcoin its value will very rapidely converge to nil. Because there's nothing to back up its value, it will stay there and never recover, and will be remembered as the 21st century tulip bulb.

On the other hand take gold: as a metal, it has little practical use (compared to its availability, it's not that scarce), yet its value is still up there after several thousand years of use. Why? Because there's a consensus that it's worth something, and trust that this value will remain (and even go up) in case of war/disaster/etc. Bitcoin could be a new gold. That's highly hypothetical.

I've speculated that it might be related to ransomware picking up in recent years. In particular, wannacry and notpetya coincided with some of bitcoin's surges in price.

Before this, purchases with Bitcoin not for investment purposes were niche in the illegal or attempts at regular purchases that only involved a few users. After these large-scale attacks, Bitcoin has basically been forcibly introduced to the populace at large to (possibly) retrieve their data.

I could argue that this has finally attached Bitcoin's value into something more than trust: data. Hence, bitcoin's value is mirroring the value of another increasingly valuable commodity.

Around November 16th there will be a fork to a new coin Bitcoin2x. The moment this happens markets will put the same amount of Bitcoin you have in Bitcoin2x to your wallet. I think at least for this month this is the sole reason the prices are exploding.

I'd wonder how much of that is new money poured into the ICOs. Selling something in the crypto-world usually means trading it for BTC. So I'd imagine all crypto money finds it's way into bitcoin eventually.